The invention relates to a gear pump with variable throughput volume furnished with two meshed gears with external toothing, which are rotatably held in the working chamber of a pump housing, where at least one of the two gears can be driven by a drive shaft and where one of the two gears, preferably the driven gear, can be shifted in the direction of its axis.
Conventional gear pumps with two meshing external gears have a driving gear which is driven from a drive shaft and is driving the second gear. Besides the tooth profile and the number of revolutions per minute of the pump the meshing width determines the throughput volume of the gear pump. Losses, which occur due to the clearance between the gear tips and the pump housing and due to the play allowed for the gap at the front faces of the gears, will affect the efficiency of the gear pump. Gear pumps of this kind are usually employed as oil pumps in internal combustion engines. Conventional oil pumps are coupled to the engine crankshaft at a fixed speed ratio by rigid, non-variable coupling means such as chains, toothed belts or toothed wheels. As engine speed increases the rpm of the oil pump will also increase and thus also the throughput of the pump. Oil pumps are usually designed to guarantee oil supply of the internal combustion engine in the worst case over the total speed range, that is at idling speed with the largest gap cross-section in the bearings, taking into account all additional oil consumers of the engine such as pistons, spray nozzles for piston cooling, turbochargers, etc. Given this design it follows that at higher engine speeds the oil pump will supply an oil volume which is many times greater than that actually required at higher engine speeds. Adapting the oil volume to the amount actually needed in a given engine state is conventionally done by pressure control and discharge of the superfluous amount of oil into the oil sump, or by recirculating the oil into the input passage of the pump. Since the gears of the pump will constantly deliver the maximum volume of oil they constantly require the same high input of driving power, independently of the actually needed output volume. This will have a disadvantageous effect on the efficiency.